Process for catalytically cracking pyrolysis condensates



Sept. 5, 1967 G. F. HORNADAY ETAL 3,340,178

PROCESS FOR CATALYTICALLY CRACKING PYROLYSIS CONDENSATES Filed Aug. 25,1964 I N VE N TORJ' fieargeflfiforlzaddy BY 17001 D. No]! United StatesPatent Office 3,349,173 Patented Sept. 5, 1967 3,340,178 PROCESS FGRCATALYTICALLY CRACKING PYROLYSIS CONDENSATES George F. Hornaday,Wallingford, and Henry D. Noll,

Philadelphia, Pa., assignors to Air Products and Chemicals, Inc.,Philadelphia, Pa., a corporation of Delaware Filed Aug. 25, 1964, Ser.No. 391,887 4 Claims. (Cl. 20-S89) This invention relates to thecatalytic cracking of pyrolysis condensates and more particularly to aprocess for the preparation of gasoline from a cracking stock comprisingsteam-cracked naphtha and gas oils obtained from crude petroleum.

Steam-cracked naphtha having a boiling range, for eX- ample, of 30-250"C. is obtained as a by-product when petroleum naphtha is cracked in thepresence of steam at elevated temperatures for the production ofethylene and propylene. Although steam-cracked naphtha has a good octanerating, its potential as a blending stock for gasolines has not beenreailzable. A high unsaturates content (particularly olefins anddiolefins which tend to form gum-like polymers, espectially when heated)has materially restricted the quantity of steam-cracked naphtha blendedinto motor fuels.

It has now been discovered that a blended cracking stock can be preparedfrom steam-cracked naphtha and gas oils obtained from crude petroleumwithout requiring pretreatment of the steam-cracked naphtha. Thisdiscovery permits the utilization of an otherwise unsaleable by-productby a noved method without affecting product quality of the gasolinesproduced which typically have F-1 octane values in the range of 88 to94, F-l clear and 95 to 99 F1 plus 3 cc. TEL. Moreover, use of theblended cracking stock does not materially alter the rate of coking orcatalyst deactivation in the catalytic cracker.

In accordance with the present invention crude petroleum, which maycontain substantial amounts of sulfurous materials such as West TexasCrude, Kuwait Crude, Baxterville Crude, Wafra Crude, etc., is subjectedto crude distillation and hydrodesulfurization. Gas oils (i.e., liquidhydrocarbons boiling about the gasoline boiling range) thereby obtainedare then blended with up to 30 Weight percent and preferably 5 to 30weight percent steam-cracked naphtha and catalytically cracked in amoving bed unit without further treatment.

The invention is clarified by reference to the following descriptionread in connection with the drawing. In this description all percentagesare by weight and are based on the crude petroleum charge stock unlessotherwise noted.

Referring tothe drawings, wherein the general layout of a refinery isdiagrammatically illustrated with omission of various pieces ofapparatus not considered necessary to an understanding of the invention,crude petroleum charge stock consisting of 40% Khafji and 60% Gach-Saranis introduced along line to distillation Column 11. Several fractionsare obtained from the distillation column, including (1) a 3% gasfraction in line 14 obtained from line 12 and separator 13, (2) a 7.4%light naphtha fraction in line 15 obtained from line 12 and separator13, (3) a 12.2% heavy naphtha fraction in line 16, (4) a 7.5 kerosenefraction in line 17, (5) a 19.9% diesel oil fraction in line 18 and (6)a 50% bottoms fraction comprising heavy gas oil in line 19. The keroseneand diesel oil fractions are combined and passed through line 20 intohydrodesulfurizer 21. The thus-treated material is then passed throughline 22 into fractionator 23 where it is separated into a 0.075%

gasoline fraction in line 24, a 7.5% kerosene fraction in line 25, a 16%diesel oil fraction in line 26 and a gas oil fraction in line 27.

The bottoms fraction in line 19 containing about 3.28% sulfur is passedin whole or in part through line 28 into vacuum tower 29. In theillustrated embodiment, approximately 56% of the bottoms fraction ispassed into vacuum tower 29 and the remaining portion in line 53 isutilized as fuel oil.

Asphalt having a 3.9% sulfur content is removed from vacuum tower 29 byline 30. Vacuum gas oil, on the other hand, is recovered from vacuumtower 29 and passed through line 31 into hydrodesulfurization unit 32.Vacuum gas oil from line 31 is circulated through line 35 to efiect aheat exchange with the desulfurized vacuum gas oil in line 33. Hydrogenis then removed in line 38 from the gas oil following its transmissionfrom hydrodesulfurization unit 32 via lines 33 and 36 to high pressureseparator 37.

The combined effect of heat exchanger 34 and separator 37 eliminates thenecessity of fractionating the gas oil in line 39 which is combined withthe gas oil from line 27. The combined gas oil stream (line 40) isfinally blended with steam-cracked naphtha from line 4-1 in an amount of5 to 30 weight percent steam-cracked naphtha based on the weight of thegas oils in line 40. Characteristics of the steam-cracked naphtha areshown in the following table:

In the illustrated embodiment about 27.6% steamcracked naphtha is addedto the gas oil and this blended cracking stock is passed through line 42into a Houdritlow moving bed catalytic cracking unit 43. Houdriflowcatalytic cracking is well known in the art and has been widelydisclosed in the literature. For example, see Hoge, Houdriflow, thePetroleum Engineer, April 1954.

The resulting products from the catalytic cracking of the blended stock(line 44) is then fractionated in fractionator 45 to obtain an overheadfraction in line 46, a 11.8% light recycle fraction in line 51 and a23.5% heavy recycle fraction in line 52, based on the blended crackingstock in line 42 at 55% conversion. The overhead fraction is separatedin separator 47 into a 5.9% fraction containing C and lighter materials(line 48), a 10% C fraction (line 49) and 54% C gasoline fraction (linebased on the blended cracking stock in line 42 at 55% conversion.

It is to be understood that the foregoing is illustrative of a singlepreferred operation in accordance with the invention which makespossible the recovery of gasoline of low sulfur content and relativelyhigh octane value.

In addition to gasoline, the C and C light products are rich inunsaturates and may be further processed for the production of alkylate,polymer gasoline or used in the petroleum industry.

A substantial investment saving in processing equipment is realized bythe present invention. Not only does the present procedure eliminate thenecessity of a fractionator for treating the desulfurized vacuum gas oilbut the presence of two hydrodesulfurization units (21 and 2) furthereliminates the necessity for separate desulfurizer units in each of theproduct lines, e.g., in lines 24 to 26and 48 to 52. This latter featureis of particular importance with'respect to gasoline fractions which areextremely difficult to desulfurize without loss of octane rating throughthe hydrogenation of unsaturates.

Typically, desulfurization is accomplished by treating an oil in vaporphase with a hydrogenation catalyst under moderate conditions oftemperature and pressure in the presence of a large excess of hydrogen.Although the vapor phase process is theoretically applicable to thedesulfurization of any hydrocarbon oil, from a practical standpointvapor phase operation is limited tov the desulfurization of lighthydrocarbon oils such as gasoline, kerosene, diesel oils, etc., whichare easily vaporized without decomposition.

Desulfurization of the vacuum gas oil in the described process isaccomplished in the liquid phase over a 0.8 to 2.4 mm.cobalt-molybdenum-alumina catalyst. Operating conditions are maintainedbetween 355 to 430 C., a pressure of 500 to 800 p.s.i.g., a space rateof 0.5 to 2.5 LHSV and a hydrogen recycle rate of 4000 to 6000s.c.f./bbl. For a vacuum gas oil having the properties set forth in thefollowing table, it has been calculated that essentially none of the oilwould be vaporized at the operating conditions present inhydrodesulfurizer 32.

Vacuum assay, (1.:

The effect of hydrodesulfurization on the catalytic cracking of vacuumgas oil is shown in the following table. Operating conditions for thecatalytic cracking were 480 C., p.s.i.g., 10 weight percent steam and a4 catalyst/ oil ratio.

Desulfu- Gas Oil rized Gas Oil Coke Yield, Wt. Percent 3. 9 3. 9Conversion, V01. Percent (to fuel oil, gasoline,

gas and coke) 56. 7 69. 6 Gasoline, Vol. Percent (385 F. at 90%) 31.540. 5 04's Vol. Percent 7. 6 12.9 Sulfur, Wt. Percent (after removing H5 and free sulfur):

Charge Stock 2. 55 0.36 Gasoline 0. 34 0. 05 Octane of Gasoline:

F-l Clear 90.5 92.0 F1 -|3 cc. T.E.L 95.6 97. 5

Thus at a fixed coke yield of 3.9 weight percent, conversion (to fueloil, gasoline, gas and coke) was 13 volume percent greater for thedesulfurized gas oil. This increased conversion resulted in an increasedgasoline yield from 31.5 to 40.5 volume percent. Moreover, the gasolinefrom the desulfurized gas oil had a significantly lower sulfur only suchlimitations should be imposed as are indicated in the appended claims.

What is claimed is:

1. A process for the production of gasoline which comprises distilling acrude petroleum to obtain heavy gas oil, a kerosene fraction and adiesel oil fraction; subjecting the kerosene and diesel oilfractions tovapor phase hydro-desulfurization; fractionating the desulfurizedkerosene and diesel oil fractions to obtain a light desulfurized gasoil; 'desulfurizing said heavy gas oil in the liquid phase preparing asteam-cracked naphtha containing troublesome amounts of diolefins as aby-product of the steamcracking of naphtha to produce gaseous olefins;preparing a steam-cracked naphtha containing troublesome amounts ofdiolefins as a by-product of the steam-cracking of naphtha to producegaseous olefins; blending said steamcracked naphtha in an amount fromabout 5 to about30 weight percent with the combined desulfurized gas oilobtained by mixing the light desulfurized gas oil from the vapor phasedesulfurization and the heavy desulfurized gas oil from the liquid phasedesulfurization operations; catalytically cracking the blendedsteam-cracked naphtha-gas oil material in a continuous moving bedcatalytic cracker at about atmospheric pressure and fractionating theproduct from the catalytic cracker to obtain gasoline.

2. The process for the preparation of gasoline which comprisessubjecting gas oil to hydrodesulfurization prior to catalytic cracking;preparing a steam-cracked naphtha containing troublesome amounts ofdiolefins as a byproduct of the steam-cracking of naphtha to producegaseous olefins; blending 5 to 30 weightpercent said steam-crackednaphtha with the desulfurized gas oil, catalytically cracking thesteam-cracked naphthaand desulfurized gas oil in a moving bed catalyticcracker at about atmospheric pressure and fractionating the resultingcracked product to obtain gasoline. V

3. The process of claim 2 wherein the gasoline has an F-1 clear octanevalue of at least 88.

4. In the process in which a gas oil is subjected tohydrodesulfurization and the hydrodesulfurized gas oil is catalyticallycracked to provide gasoline, the improvement 7 gas oil from the productof vapor-phase desulfurization;

subjecting the heavy gas oil fraction to liquid-phasehydrodesulfurization at a temperature from about 355 to about 430 C., ata pressure from about 500 to about 800 p.s.i.g., at a space rate fromabout 0.5 to about 2.5 liquid volumes per volume of catalyst per hour inthe presence of hydrogen rich recycle gas at a rate of about 4000 toabout 6000 standard cubic feet of gas per barrel of heavy gas oil toprovide a heavy desulfurized gas oil; mixing the light desulfurized gasoil and heavy desulfurized gas oil to provide a blended gas oil;subjecting naphtha to steam cracking for the preparation of gaseousolefins and a by-product diolefin-containing naphtha; preparing amixture of said blended gas oil and from 5% to 30% of saiddiolefin-containing steam-cracked naphtha; subjecting said mixture to acatalytic cracking zone at about atmospheric pressure; and separating bydistillation from the products from the catalytic cracking zone a stablenaphtha having no troublesome amounts of diolefins.

References Cited UNITED STATES PATENTS 2,914,459 11/1959 Mills et a1208-130 6 3,147,210 9/1964 Hass et a1. 208210 3,155,608 11/1964 Hopperet a]. 20889 3,240,695 3/1966 Hamner et a1. 208-130 5 DELBERT E. GANTZ,Primary Examiner.

SAMUEL P. JONES, Examiner.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No 3 ,340,178 September 5 1967 George F. Hornaday et al.

rror appears in the above numbered pat- It is hereby certified that ePatent should read as ent requiring correction and that the said Letterscorrected below.

Column 1, line 22, for "reailzable" read realizable line 32, for "noved"read novel line 53, for "drawings" read drawing column 2, after line 34,insert 5%--3E column 4, line 20, beginning wlth "preparing" Strike outall to and including "olefins;" in line 22, same column 4.

Signed and sealed this 30th day of Jul 1968.

(SEAL) Attest:

EDWARD J. BRENNER Edward M. Fletcher, Jr.

Commissioner of Patents Attesting Officer

4. IN THE PROCESS IN WHICH A GAS OIL IS SUBJECTED TOHYDRODESULFURIZATION AND THE HYDRODESULFURIZED GAS OIL IS CATALYTICALLYCRACKED TO PROVIDE GASOLINE, THE IMPROVEMENT WHICH INCLUDES THECOMBINATION OF; DISTILLING CRUDE PETROLEUM TO PROVIDE A NAPTHIAFRACTION, KEROSENE AND DIESEL OIL FRACTIONS AND A HEAVY GAS OILFRACTION; SUBJECTING SAID KEROSENE AND DIESEL OIL FRACTIONS TOVAPOR-PHASE HYDRODESULFURIZATION; DISTILLING TO SEPARATE A LIGHTDESULFURIZED GAS OIL FROM THE PRODUCT OF VAPOR-PHASE DESULFURIZATION;SUBJECTING THE HEAVY GAS OIL FRACTION TOLIQUID-PHASE-HYDRODESULFURIZATION AT A TEMPERATURE FROM ABOUT 355 TOABOUT 430*C., AT A PRESSURE FROM ABOUT 500 TO ABOUT 800 P.S.I.G., AT ASPACE RATE FROM ABOUT 0.5 TO ABOUT 2.5 LIQUID VOLUMES PER VOLUME OFCATALYST PER HOUR IN THE PRESENCE OF HYDROGEN RICH RECYCLES GAS AT ARATE OF ABOUT 4000 TO 6000 STANDARD CUBIC FEET OF GAS PER BARREL